1. Field of the Invention
This invention relates to a data carrier system.
2. Description of the Background Art
Such data carrier systems are known for example in the form of contact-type or contactless chip cards, security labels, luggage labels or vehicle keys. The control unit, data memory and part of the means for permitting information exchange are usually integrated on a chip in the form of an electronic circuit. Information exchange can be effected for example via external contacts or via inductive or capacitive antennas with a corresponding transponder device.
External access units transmit and receive information to and from the data carrier system and frequently also supply it with energy. They are usually referred to as readers despite the possibility of bidirectional communication.
Certain data carrier systems, such as cash cards, access cards or vehicle keys for activating the driving mode, deactivating immobilizers or actuating locking systems, involve the storage of security-relevant data, such as secret key data. Due to encrypted storage, such security-relevant data cannot be spied out as long as the electronic circuit configuration of the chip is not in the operating state. An attack on the security-relevant data stored in a chip consequently requires that the electronic circuit configuration of the chip is in the operating state and the security-relevant data are stored in decrypted form.
Secret data in a data carrier system can be attacked via the external contacts of a contact-type data carrier system or via the radio link of a contactless data carrier system. However, there are quite a few measures not explained in any detail here for preventing such attacks from permitting access to secret key data or other security-relevant data. A further possibility for spying out data is to attack the chip, for example by using focused ion beams or electron microscopy to determine the charge state of memory cells or the data flow on data buses. Such an attack on the chip usually requires removal of the chip or at least of a chip module with chip and contacts or trans-transponder antenna from the card. For this purpose the card is usually greatly damaged or the card material chemically dissolved.
German laid-open print DE 197 38 990 A1 discloses a chip card having a security device containing an oscillator for transmitting a security signal. The signal emitted by the oscillator is excited by a capacitance arrangement which is part of the module and produces a value that is characteristic of the sensed capacitance. Said signal is detected with a detection means, evaluated by an evaluation means, and the function of the card is enabled when the sensed capacitance matches the chip-specific capacitance.